Overload relay



G. O. WlLMS OVERLOAD RELAY Feb. 9, 1932.

Filed Aug. 8, 1928 .2 Sheets-Sheet l l l-: Z J

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OVERLOAD RELAY Filed Aug. s, 1928 2 sheets-sheet 2 M ff/ /2 MEM/6@ Patented Feb; 9, 1.932

UNITED ls'rxrrfs PATENT OFFICE GUSTAV 0. WILIS, OF MILWAUKEE, WISCONSIN, ASSIGNQR, :BY MESNE ASSIGNMENTS, T .ALLEN-BRADLEY COMPANY, 0F MILWAUKEE, WISCONSIN, A CORPORATION OF W'ISCUNSIN' Application led August 8, 1928. Serial No. 298,300.

This invention Vrelates particularly to an overload relay of they thermally actuated type and has as an object to simplify and improve the general construction of such relays.

Thermal relays heretofore in use have functioned satisfactorily where the operating over-load has been suiicientlyhjgh as approximately 600% but their slow `response when usedwith such relatively smaller overloads asv 100 to 150% `due to the temperature rise being insufficient, has been extremely objection'able and this invention, therefore, contemplates as an object the provision of ,an improved thermal over-load relay embodying a heating element, the characteristic of which is vsuch that its resistance inl creases rapidly as its temperature rises thus insuring the desired quick operation of the relay upon the occurrence of over-loads of lesser degreethan that heretofore operated with.

.Another object of this invention resides in the provision of an improved over-load relay of the character described in which the heating element is formed of iron or any other material having a marked positive temperature coelicient whereby its resistance rapidly increases as its temperature rises.

`A further object of this invention resides in the provision of an improved over-load 'relay of the character described which may be readily reset in a relatively short time after the over-load occurs.

And a still further object of thisv invention resides in the provision of an improved overload 'relay of the-character described which may be conveniently enclosed in a suitable housing and which has means actuated from' the exterior o f the housing for resetting the device.

With the above and other objects in view which will appear as the description proceeds, my invention resides in the novel construction, combination and arrangement of OVERLOAD RELAY REISS-UED In the accompanying drawings, I have illustrated one complete example of the physical embodiment of my invention constructed according to the best mode I have so far devised for the practical application of the .Figure 1 on the plane of the line 2--2;

Figure 3 is a fragmentary top plan View of the over-load relay removed from its housing and with a portion thereof broken away to more clearly illustrate structural details;

Figure 4 is an enlarged side view of the over-load relay shown detached from the housin and its mounting panel withy parts thereo broken away and in section;

Figure 5 is a diagrammatic view illustrating my improved relay incorporated in a simple motor circuit, and y Fi re 6 is a diagrammatic view illustrating t e over-load relay as applied to a three phase starting system for motors.

Referring now more particularly to the accompanying drawings, in which like nuc lined with insulating material 7.

The mechanism of the over-load relay is mounted on the base 6 and is carried by a bracket member 8 having a vertical attaching portion 9 by which it is secured to the base 6. From the-upper end of the portion 9 the bracket is directed laterally, as at 10, and then upwardly, as at 11, and back again in a plane parallel to the part 10, as at 12, forming substantially a U shaped structure, the part 12 being shorter than the part 10. As illustrated in Figures 2 and y3, the vertical attaching portion 9 is of less width than that of the remainder of the bracket and the part is reduced inwardly toward the narrower width of the member 9L The bracket 8 is mounted medially on the base 6 and substantially in line with the up- 32 to mount a ratchet 35.

per part 12 thereof and carried by the base 6 is a switch member 13. The switch member 13 constitutes the movable element of a disconnecting or circuit breakin@ switchrand is formed of a strip of yieldable condu-cting material having a contact 14 secured to its outer end and having its inner end bent back in substantially hairpin fashion to be impinged between the adjacent portion of the ase 6 and one vleg of a substantially U shaped terminal 15. A screw 16 passing through an aperture in the base 6 is threaded in the leg of the terminal 15 to connect the same therewith and the opposite leg of the terminal 15 is provided with a screw 17 by which a lead 18 entering the housing through aligned apertures therein and in the base 6, is electrically connected with the switch member 13.

The movable contact 14 cooperates with a stationary or fixed contact19 secured 0n the base 6 by a screw 2O passing through an aperture in the base and threaded in the terminal, arc shields 21 being provided at each side of the contacts as is customary. The contact 19- is connected with a lead 22 through a ma netic blow-out coil 23, one end of which 1s connected with the contact 19 at its attaching screw and the other end with a terminal 24, at the back of the insulating base 6 by a conductor, n'ot shown. One end of a coil of resistancewire forming aheating element 25 iS secured to the terminal 24 and the other t0 a terminal 26 connected with a terminal 27 at the back of the base 6 by a conductor, not shown, with which the end of the lead 22 is connected. y f

The switch arm 13 is held in its position closing the switch by the mechanism of the relay now about to be described. The part 10 of the bracket 8 is .provided with a threaded aperture 28 in which a bushing 29 formed of suitable heat resisting refractory material is loosely threaded, and the space therebetween being filled with a suitable heat resisting cement 30. The cement 30 also lills a space left between the flange 31 of the bushing 29 and the upper face of the part 10 and encircles the flange to secure the bushing onto the part l0.

A substantially cup-shaped washer 32 is positioned above the flange 31 of the bushing and is secured thereto by like cement 30, the bushing being apertured, as at 33, and having a hollow stem 34 secured in its aperture with its major portion extending below the part 10 of the bracket and its top portion extending through the aperture of the washer The ratchet 35 has a downwardly project- ,f ing annular boss or flange 36 of a diameter 6J metal of relatively low meltingpoint fills the space between the stem 34 and the aperture of the ratchet and the recess 37 of the washer to normally secure the ratchet 35 to the stem 34. The heating element or coil 25 is wound about the downwardly projected portion of the' stem 34 in close thermal relation thereto so that when an over-load occurs its heat, due to the excessive current passing therethrough, is conducted to the metal 38 which melts and frees the ratchet. This freeing of the ratchet permits means to be later described to open the switch 13 and break the circuit with which the device is used.

The' heating element 25 is preferably formed of iron wire as iron has a positive temperature coefficient and its resistance when heated increases so that the device is quickly brought to a temperature at which the solder melts to permit opening of the switch 13.

The upper part 12 of the bracket is apertured in axial alignment with the threaded aperture 28 of part 10 and that portion adjacent the aperture is reduced in width to form shoulders 39 extending to each side of the frame as best illustrated in Figure 2. A stud 40 having a bearing portion 41 is secured in the aperture of the part 12 of the bracket by a nut 42`and the bearing portion 41 thereof extends below the bracket part 12 and through a bushing 43 on a switch arm actuating lever 43 to medially pivotally mount the lever," the inner arm 44 thereof being provided with a roller 45 of insulating material pivotally mounted thereon by a stud 46. The roller 45 engages the switch arm 13 to maintain the same in its closed position.

The outer arm 47 of the lever 43 has a stud 48 secured thereto at a point spaced from its pivotal mounting 41 to provide means for mounting a pawl 49, the pawl having a bushing 50 secured thereto in which the stud 48 is positioned. The pawl 49 is arranged'to engage the teeth of the ratchet 35 and is yieldably urged to such engagement by a pawl spring 51 having one end engaging t e outer edge of the pawl and being medially coiled about the bushing 50 and having its other through the circuit with which the device isl used is within a predetermined value. y

A spring 53, aving its medial portion coiled about the bushing 43 of the lever 43 and having one end 54 hooked behind one shoulder 39 of the part 12 ofthebracket with its other .end 55 engagin the bushing 50, normally yieldably urges tile lever 437 toward inactive position, tending at all times to produce rotation of the ratchet on the stem 34 to permit the roller to move away from the switch arm 13, to a position illustrated in dotted lines in Figure 3.

As long as they circuit is operatin under normal conditions the parts maintain their operative positions but when an over-load occurs, the heating element 25 heats the stem 34 to melt the solder and thus free spring 53 to turn the ratchet 35 and permit the lever 43 to assume its dotted line position shown in Figure 3, breaking the circuit at the contacts 14 and 19. As the circuit is thus broken, the element 25 quickly cools and the solder again sets and secures the ratchet 35 to the stem 34. Resetting of the device is then accomplished by moving the arm 47 of leverf43 to move the switch arm 13 to its closed position where it is held by the engagement of' the pawl 39 with one of the teeth of the ratchet 35.

A cover 56 suitably secured to the housing completely encloses the device and a resetting lever 57 having a stud 58 extending outwardly through the-cover and with an actuating knob 59 positioned thereon provides means for moving the arm 47 of the lever 43 to the right with respect to Figure 2 to reset the mechanism. The arm 57 is normally held in its inactive position byl a spring 69 coiled about the pivot rod 58 and having one end ,Y engaging a projection 61 carried by the arm.

In Figure 5 is illustrated diagrammatically a simple motor circuit in which the overload relay described is incorporated. rll`his circuit includes the lead 18, terminal 17, switch arm 13, and its contact 14 which is normally engaged with the contact 19 being held in this position by the switch arm actuating lever 43. As above described the contact 19 is connected with a terminal 24 through a magnetic blow-out coil 23 and the terminal 24 has one end of the resistance element 25 connected thereto, the other end thereof being connected Ywith a terminal 26. From the terminal 26 the circuit extends to the terminal 27 and then to the motor M through the lead 22 and from the other side of the motor M a conductor 62 connects with the other side of the source of supply. In Figure 6 two over-load relays are included in the control circuit of an automatic motor starting switch which includes lead-in conductors 63, 64 and 65 which connect with contacts adapted to be engaged with the switch arms 66, 67 and 68 of a magnetically actuated switch 69 to close the circuit of its motor M through conductors 70, 71 and 72.y The heating elements 25 in this instance are inserted in series` with the conductor 7 0 and the conductor 72.

The switch 69 is closed by energization of a solenoid coil 73, the circuit of which extends rom the lead-in conductor 65, through a conductor 74 to a terminal 75, conductor 7 6 to one side of a starting switch 77 from the other side thereof through a conductor 78 to one side of a stopping switch 79 from 'the other side thereof through the lead 18 to terminal -17 From the terminal 17, the circuit continues through the switch 13, contacts 14 and 19, through a conductor 89 to one side of the solenoid coil 73, through the coil, through a conductor 81, through the second switch 13, its contacts 14 and 19 and through a conductor 82 to the side 63 of the line. Initial closing of the. starting switch 77 energizes the coil 73 Y which closes the switch 69 thus bridging the control circuit at the contact through switch arm 83 which is connected with the ar side of the starting switch 77, by a conductor 84 thus maintaining the control circuit closed until manual opening thereof by actuation of the stoppingvswitch 79 or by opening of the switch 13 of either over-load relay.

From the foregoing description taken in connection with the accompanying drawings, it will be readily apparent to those skilled in the art to which an invention of this character appertains that ll provide an over-load relay which is simple in construction, which permits ready resetting thereof and one in which the heating element is formed of material having a positive temperature coeiii-4 cient and in which the resistance thereoF builds up as its heat increases.

What l claim as my invention is:

1. lln an overload relay of the character described, a circuit closure normally yieldably urged to one position, a mounting member, an actuating member carried thereby and adapted to hold the cireuit closure in its other position, a tubular stem carried .by said mounting member, a locking member on said tubular stem, thermally responsive means normally securing the locking member Afixed to the stem, means connectin the actuating member with the locking mem er to normally maintain the actuating member in its'position urging the circuit closure to said other position, and a heating coil surrounding the stem whereby an increase in temperature of the coil is readily conducted to the thermally responsive means securingthe locking member in fixed position through the tubular stem to free the locking member and permit the actuating member to move to a position releasing the circuit closure for movement to its first-mentioned position.

2. ln an overload relay of the character described, a substantially U shaped supporting frame, an actuating member pivotally carried by one arm of the frame and adapted to hold a circuit closure in a predetermined position, means at all times yieldably urging said actuating member to a position permitting the circuit closure to move out of its predetermined position, means for holding the actuating member against its urging means o member to` 'cause comprising a mounting stem carried by the other arm of the frame in axial alignment with thepivotal mounting of the actuating member, a ratchet wheel on the mounting stem, thermally responsive means normally securing the ratchet wheel to the stem, a pawl carried by the actuating member and engaging the ratchet wheel, and a heating element surrounding the stem and adapted upon heating to raise the temperature of the thermally responsive means by radiation through the mounting stem to release the ratchet wheeland free the urging means of the actuating member to cause it to move the actuating member out of its normal position.

3. Invan overload relay of the character described, the combination with a circuit closure normally yieldably urged to a predetermined position, of an actuating member for releasably holding the circuit closure in its other position, means at all times yieldably lurging the actuating member to a position permitting the circuit closure to move to said predetermined "position, means for holding the actuating member against "its urging means, comprising a locking member, thermally responsive means normally securing the locking member against movement, means connecting the actuating means with the locking member, a heating element adapted upon heating to raise the temperature ofthe thermally responsive means to release the locking member and free the urging means of the actuating member to move the actuating member out of its operative position, and

means mounting the actuating member andthe locking member upon a common axis.

4. In an overload relay of the character described, the combination with a circuitI closure normally yieldably urged to a predetermined position, of a supporting frame having overlying arms, an actuating member pivotally carried by\one arm and adapted to hold the circuit closure against movement t0 its predetermined position, means at all times yieldably urging said actuating member to a position permitting the circuit closure to move to its predetermined position, means for holding the actuating member against its urging `means comprising a mounting stem carried by the other arm of the frame, a ratchet wheel on the mounting stem, ther- `mally responsive means `normally securing the ratchet wheel to the stem, a pawl canried by the actuating member and engaging the ratchet wheel, and ai heating element surrounding the stem and adapted upon heating to raise the temperature of the thermally responsive means by radiation through the mounting stem to release the ratchet wheel and free the urging means of the actuating it to Amove the actuating memberabont its-pivotal mounting and out ofoperative" position, and said 'mounting stein and ratchet wheel being in axial alignment with the pivotal mounting of the actuating member., I

5. In a protective device of the character described,.; a switch member biased toward` one position, a member journalled for movement about a fixed axis and having a part engageable with the switch member to maintain the same in another position, means for releasably holding the journalled member in a position maintaining the switch menber in said other position, said meansI including a heat conducting stem in axial alignment with the axis about which the journalled member is movable and a ratchet normally secured on said stem by fusible metal, a heating element surrounding the stem and adapted to raise the temperature of the fusible metal to its fusion point whereupon the ratchet is released for movement, and means operable upon release of the ratchet for quickly moving the j ournalled member to a position freeing the switch member for movement to its first mentioned position. Y

6. In a protective device of the character described including a switch, means for maintaining the switch closed, including a laterallyextended mounting member, a bushing of heat resisting material carried by the mounting member, ixed in said bushing with its end portions lextended above and beneath the mounting member, a ratchet secured on the upper en portion of the stem by fusible metal, a conuection between the ratchet and the means for maintaining the switch closed for releasably holding said means in its operative position, and a heat-ing element coiled about the lower end portion of the stem beneath the mounting member whereby heat from said heatin element is conducted to the fusible meta through the stem, the release of the ratchet upon the temperature reaching the fusion point of the fusible metal releasing the means for maintaining the switch closed and permitting the same to move to .an inoperative position.

In testimony whereof I have hereunto afiixed my signature.

GUSTAV O. WILMS.

a heat conducting stem 

